Hydraulic fluids



Patented July 25, 1950 HYDRAULIC FLUIDS 1 Char-les W. Montgomery: andWilliam L Gilbert,

Oakmont; and Robert E. Kline, ienna 'lown- Research Developmentddompany,r Pitts- 1 .burgh, .-1a.-, a corporation .01 Delaware I *No Drawing Arnti =..1.Serial N0.*7 8

i t v s16,- -Claims.

,-';1his:;invention1 relates toi :hydraulic -fluids,.and more;particularly to fluids for "11863111 -*hydraulially operated-apparatus,wsuchas brake :mechanlsms, fluid flywheels, shock u absorbers,controlmechanisms and similar hydraulically operated quipment.

V arious Jfluids have previouslvbeen proposed for use inr hydraulicsystems ashydraulic power ransmission mediator the like; In a greatnumer ofthe previously. proposed-fluids, there have een manydisadvantages attendant to their use, A uch,-;aslcorrosive and degradingeffects'ofsuch fluids -on metaland rubber-parts of the hydraulicvequipment, actendency towardsqvolatilization at a perating;temperatureswlack' oi nsuificient lubriatieawm ti etc.

It -is an object of this-inventiomtherefore, to provide a-hydraulicfiuid which overcomes the @disadvantage of many of the priorartmaterials.

51b is a further object of this invention to provide hydraulic fluidswhich have general utility if under variable operating conditions.

-,-These and other objects are accomplished by the-present inventionwherein we provide as a hypdraulic fluid for hydraulic equipment aliquid 1-; omprising a substantially neutral ester of a monohydricalcohol and the mixture of acids obg tained by the oxidation withgaseous oxygen of an aqueous alkaline slurry of a finely divided car----bonaceous material selected frcm'the group conistingof. coal and cokeobtained by the carbonzation of coal at temperatures below 700 C. For-.convenience, the acids described above are here-'-,-.,inafterereferred to as coal acids.

w We have found that the substantially neutral ,trnonohydric alcoholesters of the mixture of :coal -acids described above provide excellenthydraulic -i-iuids,whlch are characterized by general utility wunder awide variety of operating conditions. These esters may be readily andcheaply prepar ed,-and therefore are an attractive source of "hydraulicfluids.

As has been stated, the acids usedin the preparationof our new hydraulicfluids-,areobtained by the oxidation with gaseous oxygen 40L; an aqueousalkaline slurry of a finely divided carbonaceous material selected fromthe group consisting' 01";0031-8111'1 cokeobtained by the carbonizationof coal at temperatures below 700? C Suitable coals. compriseanthracite, bituminous,

sub-bituminous, lignite and other low grade coals. Suitable cokes arethose produced by the carbonization of a coal at a temperature below700C; in a manner known tothe art. 1 If the cokes are pro- 12-.':Z'I.beC0me'r graphi-ticiandrunsnitable; for .thezmroduction or coalacids axsatisfaetory gyield. The;.fbllowingvis an exampleioftheapreDfl-ration: of the-coal acids. Finely groundibituminous: coal,:alkali; :such;v as sodium hydroxide and qwatemare mixed}; in anickel-lined autoclave:equipped -with a: turbomixer and with meansfor.heatin zandncoolinggthe charge. The iamountiofialkali:usecL is,inexc.ess 0 of that requiredrcfimpletely-q towneutra liz all: ofrthegcoallgacids lfqtmem in" thew-oxidation ,p cess. "'Bywayofjyexamplenthe proportion l'ofrthedncgredients 'may-wbe" '15 -pQundSof coal, 15cgallons -of-;. ;water and 45,: pounds' jof causticisqdani'Ihe 15 charge wis heateduand irthenwoxysen is cbubbled therethrough.r-w'lhe temperature of'thej'charge is maintained: from-- 200? to300 Cc;at a total -pres- 1surewof= from.500 ;to@1 200;p0unds per-squarerinch.The reaction? is; exothermic and therltemperature: 3151f main ained "Wit1hl1'1.3th8ijimit-sfi'statedjby P cooling; zsucheas by passinawaterithroughssanrinternal' COO1jiI1g"CO -1Zfin:the autoclave; zTheloxida- I '1 :tion is contin-lled 'xuntil -=all of; the i, carbonaceous.a-material; oi -the coal passes intossolutionrand usu- .-allyrequires-between" 21 31116. 3 hours l-Hali-ofiathe carbon of the coalisroxidizedeto-porganicizaeids wand the remai-nderwto carbon-dioxide.i-iAtzzthe com letion-ofrtheoxidation thechargegisrcooled to about L10g0.: and is? discharged: rfromstherz auto- 0. clave. The ash ofathe coalwhich is *rlargelyrun- -attacked; is removed: byvfllteringcthroughzalifilr press. l '2 i' her l er lrrprqduct aisacan :ealkaline-esclutioncontaining the sodium salts of the organ \gaeids obtained bymthe:oxidation: of thew coal. Enough sulfuric acid-is:added; to this'solutior'mto, liberate i the free vacids. Any-:insoluble material:appearing: after qacidificat-ion withsuliuric acidadszremoved'by %fi;ltering.;-; 'l'herlfreewoalracids obtained 5 are water-soluble and mayconveniently be robstained from, their; solutionaimwater;-by;nextractionwith a water-immiscible organic solvent. I'IEFOI' exampleqmethyl ethylketone may-bemseddor this purpos in e; nzthe: p esence; .oifrthe sodium;su fate produced by the acidification withpsulfuric acid, methyl ethylketone is water-immiscible. Thelextract phase may then be transferred toa still for recovery of the bulk ofathe solvent, and the. productremaining in the still may. ,thenbejecl 0. to. alvacuum rotary drier forremovalofwthe remainder of -the solvent. For convenience inrsub-.sequent handling, the dried product: may; be

ground to a fine powder in a pebble mill.

*The product obtainedappears to be amixture ducedat--temperatures inexcess of "700" C., they "56"01' aromatic acids. ,This mixture is afree-iflo'wing 3 yellow powder which is hygroscopic and substantiallycompletely soluble in water. The average molecular weight of the acidsis 250 and the average equivalent weight is 80. Accordingly, the averagenumber of carboxyl groups per molecule is somewhat more than 3. Theexact nature of the acids is unknown, but they are believed to containtriand tetra-carboxylic benzene acids, as well as acids having a more,

complex nucleus than the benzene ring.

In order to obtain the hydraulic fluids of our invention, the coal acidsas obtained above are esterifled with a monohydric alcohol to producesubstantially neutral esters. Esteriflcation may conveniently be carriedout by refluxing 6 moles of the alcohol with 1 mole of the coal acidsfor several hours while continuously adding'small.

as methyl, ethyl, propyl, butyl, amyl, hexyl, octyl,

decyl, lauryl, myristyl, palmityl and eicosyl alcohols yield excellentproducts. Branched chain alkanols such as isopropyl alcohol,2-ethyl-hexyl alcohol, and the individual by product alcohols obtainedfrom the methanol synthesis may also be employed. Other monohydricalcohols which may be employed are the unsaturated aliphatic alcoholssuch as allyl alcohol, crotonyl alcohol, oleyl alcohol and the like.Alicyclic and aromatic service conditions extremely remote.

The esters of the coal acids obtained as described hereinabove present anumber of properties making them eminently suitable as hydraulic fluids.The high initial boiling points and extremely low vapor pressures of theesters, even at elevated temperatures, render any loss of thesehydraulic fluids by vaporization under As a matter of fact, the estersof the coal acids cannot be distilled in appreciable amounts by ordinarydistillation techniques and can only be partially fractionated bymolecular distillation. The esters are very stable, particularly withrespect to oxidation. They also have high viscosity indexes, high flashpoints and excellent lubricating properties. In general, the lowerstraight chain alkanol esters of the coal acids, including the octylester, have pour points sufficiently low to give them general utility ashydraulic fluids. For those monohydric alcohol esters having arelatively high pour point, such as the lauryl ester, the addition ofsolvents or diluents in the proportions hereinafter disclosed servesvery effectively to lower the pour points without materially affectingthe desirable properties of the esters. By reason of the fact that theesters are anticorrosive, they may safely be used in contact with themetal parts of hydraulic equipment without requiring the addition of acorrosion inhibitor. The esters have a high specific gravity and aretherefore excellently adapted for use as fluid flywheels. In brief, theesters of the coal acids present an aggregation of properties in asingle material which renders them particularly suitable for general useas hydraulic fluids, and in addition, it is unnecessary to add corrosioninhibitors and lubricants which are normally required to be added toprior art hydraulic fluids. Although we have disclosed the use of theesters monohydric alcohols such as cyclohexanol and of the coal acids ashydraulic fluids by thembenzyl alcohol are also suitable. Mixtures ofselves, diluents and/or solvents may be added to monohydric alcohols mayalso be employed, parthe coal esters to produce homogeneous hydraulicticularly the mixture of alcohols obtained by the fluids. When a diluentis used it will ordinarily reduction of coconut oil fatty acids andknown be present in an amount from about 5 to about commercially asLorol, the mixture of higher .45 p r cent by Weight 011 the esters of te 811 ac s molecular weight alcohols obtained as a product dependinguopn the particular requirements, in the synthesis of methanol fromcarbon such as whether a light or heavy grade of fluid monoxide andhydrogen, as well as the mixture of is required for a particularapplication. Alalcohols obtained as a by product in the synthough theesters of coal acids are soluble in a thesis of hydrocarbons from carbonmonoxide 50 wide variety of solvents, it is preferred to use andhydrogen. A preferred subgroup of monorelatively non-volatile solventsboiling in the hydric alcohols comprises the straight chain kerosenerange or above as diluents of the esters aliphatic alcohols containingfrom 4 to 12 carbon in our hydraulic fluids. Thus the lower aliphaticatoms. alcohols, such. as methanol, ethanol and propanol,

- If desired, the esters obtained as indicated and the low boilinghydrocarbons, such as benabove may be treated with lime and an adsorbentzene and toluene, are not desirable as diluents. such as fullers earthin order to purify the crude Typical solvents which may be used asdiluents product. For example, in one such treatment the are (l) theglycol ethers including the monoestcrs are stirred with 4 per cent byweight of butyl ether of ethylene glycol, the monoethyl fullers earthand 4 per cent by weight of lime at {30 ether of ethylene glycol, the'methyl ether of a temperature of 150 to 200 C., and are then ethyleneglycol monoacetate, the butyl ether of flltered. diethylene glycol andthe diethyl ether of ethylene Representative properties of some of theesters glycol; and (2) hydrocarbon solvents such as of this inventionare shown in the following light lubricating oils, gas oils, keroseneand'the table: like.

Ester Inltai%17:6B0.gfiL C. Sp Gm Visibg slljl at ViSiOS SUI at VI PourF1.t.,

' n-Butyl (crude)... greater than 27l 1.094 at 130l60 F 2,479 130 76n-Bntyl (treated 1 greater than 27l 10,210 360 92 n-Octyl (crudc)greater than 380 1.654 117 95 0 n-Octyl (treated) greater than 380"...1,820 123 94 0 n-Lauryl (crude) greater than 366.-. 0.9659 at 60l60 F l,218 116 +55 n-Lauryl greater than 366 0.9659 at 60 'l60 F 1,267 116 +501 Treated with 1611a"; earth and lime as disclose din the precedingparagraph.

The following data illustrate some of the properties of the coal acidesters containing diluents. Data for the ester per se are included forcomparison.

The hydraulic. fluids of the present invention, whether comprising theesters of the coal acids alone or in combination with a diluent asdescribed above, may be used as fluid power and transmission media inany of the common hydraulic systems wherein power is transmitted from anactuable element to an actuated element by means of a fluid, the mostcommon form of such a system comprising a. pair of variable volumechambers with, connecting conduit means, the chambers and the conduitmeans being filled with a fluid hydraulic power transmission medium. Thehydraulic fluids of the present invention may also be used in analogousequipment in which power transmission is not the primary purpose as, forexample, in power absorption systems, such as damping mechanisms, shockabsorbers and the like.

What we claim is:

l. The process which comprises transmitting power by means of a liquidcontaining a. substantially neutral ester of a monohydric alcohol andthe mixture of acids obtained by the oxidation with gaseous oxygen of anaqueous alkaline slurry of a finely divided carbonaceous materialselected from the group consisting of coal and coke obtained by thecarbonization of coal at temperatures below 700 C.

2. The process of claim 1, wherein the monohydric alcohol is an alkanolcontaining up to 20 carbon atoms.

3. The process of claim 1, wherein the monohydric alcohol is an alkanolcontaining from 4 to 12 carbon atoms.

4. The process of claim 1, wherein the monohydric alcohol is butylalcohol.

5. The process of claim 1, wherein the monohydric alcohol is octylalcohol.

6. The process of claim 1, wherein the monohydric alcohol is laurylalcohol.

L'The process of claim 1, wherein the finely divided carbonaceousmaterial is bituminous coal.

8. The process of claim 1, wherein the liquid contains additionally arelatively non-volatile diluent boiling at least in the kerosene range.

9. A homogeneous hydraulic fluid comprising (1) a substantially neutralester of a monohydric alcohol and the mixture of acids obtained by theoxidation with gaseous oxygen of an aqueous alkaline slurry of a finelydivided carbonaceous material selected from the group consisting of coaland coke obtained by the carbonization of coal at temperatures below 7000., and (2) a relatively non-volatile diluent therefor boiling at leastin the kerosene range and being present in an amount of from 5 to percent by weight.

10. The fluid of claim 9, wherein the diluent is a glycol ether.

11. The fluid of claim 9, wherein the diluent is a hydrocarbon solvent.

12. The fluid of claim 9, wherein the monohydric alcohol is a straightchain al'kanol containing from 4 to 12 carbon atoms.

13. The fluid of claim 9, wherein the monohydric alcohol is butylalcohol.

14. The fluid of claim 9, wherein the monohydric alcohol is octylalcohol.

15. The fluid of claim 9, wherein the monohydric alcohol is laurylalcohol.

16. The fluid of claim 9, wherein the finely divided carbonaceousmaterial is bituminous coal. 1

CHARLES W. MONTGOMERY. WILLIAM I. GILBERT. ROBERT E. KLINE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,390,258 Katz et al. Dec. 4,1945 FOREIGN PATENTS Number Country Date 429,175 Great Britain May 20,1935 454,628 Great Britain Oct. 5, 1936 OTHER REFERENCES ChemicalAbstracts, vol. 40 (1946), page 5223. Beilstein: vol. IX, 4th ed., page1010, and the 1st supplement thereto on page 443.

9. A HOMOGENOUS HYDRAULIC FLUID COMPRISING (1) A SUBSTANTIALLY NEUTRALESTER OF A MONOHYDRIC ALCOHOL AND THE MIXTURE OF ACIDS OBTAINED BY THEOXIDATION WITH GASEOUS OXYGEN OF AN AQUEOUS ALKALINE SLURRY OF A FINELYDIVIDED CARBONACEOUS MATERIAL SELECTED FROM THE GROUP CONSISTING OF COALAND COKE OBTAINED BY THE CARBONIZATION OF COAL AT TEMPERATURES BELOW700*C., AND (2) A RELATIVELY NON-VOLATILE DILUENT THEREFOR BOILING ATLEAST IN THE KEROSENE RANGE AND BEING PRESENT IN AN AMOUNT OF FROM 5 TO50 PER CENT BY WEIGHT.